Manila is broken is threee places, so fix them:
1) test 'test_misc' with WebOb 1.5
WebOb 1.5 was released at 2015-10-11. With this new version,
webob.exc.WSGIHTTPException() constructor now fails with a KeyError
when the HTTP status code is 0.
test_exceptions_raise() of test_misc tries to instantiate all
exceptions of manila.exception. The problem is that
ConvertedException uses a default HTTP status code of 0.
Modify the default HTTP status code of ConvertedException to 400 to
fix the unit tests.
2) Add dependency for 'testresources' that is required by migration
tests.
3) Remove 2 unit tests related to testing of oslo.policy lib
functionality that should not be tested in Manila. It started failing
because under-the-hood behaviour was changed in new realese 0.12.0
Closes-Bug: #1505153
Closes-Bug: #1505374
Change-Id: I0f28f3c3fb2c7eec1bafc3a617344990f86810cf